1. Field of the Invention
The present invention relates to a method for making a coiled or helical spring by rotating feed rollers with a wire held therebetween to feed out the wire by a given length via a wire guide to bring it in engagement with a bending die for coiling, in which a pitching tool for limiting the pitch of the coiled spring is designed such that its amount of extension can easily be adjusted, thereby easily making variously shaped spiral springs of high quality, and to an apparatus suitable for carrying out such method.
2. Statement of the Prior Art
Typical coiled springs are compression helical springs broken down into two types, (a) a straight type, shown in FIG. 13(a), and (b) a taper type varying in diameter, shown in FIG. 13(b). These compression spiral springs, now produced, are regulated in terms of the diameter of a coil, total number of turns, amount (and number) of the seat turn, free length, pitch and other factors, depending upon the purpose. Such compression helical springs have wide applications and so have to be produced in various types but in small quantities.
Such pitched compression spiral springs are produced exclusively by a bending die technique. According to this technique, feed rollers with a wire held between them are continuously rotated by given angles to feed out a wire by a predetermined length to bring it in engagement with a bending die, thereby making a coil. Used with this technique is an apparatus including a wire feed portion for rotating the feed rollers with the wire held between them by the given angles to feed out the wire by the given length continuously, a pitching tool operating portion for operating a pitching tool to limit the pitch of a coiled spring and a bending die operating portion for determining the diameter of the coiled spring.
The conventional apparatus will now be explained with reference to FIGS. 14 and 15 of the accompanying drawings.
FIG. 14 is an illustrative view showing the structure of the pitch tool operating portion, and FIG. 15 is an illustrative view showing a means for regulating the stroke of a segment gear adapted to rotate the feed rollers of the conventional apparatus.
The wire feeding portion of the conventional apparatus is of the structure wherein the rotation of a crank disk driven by a motor is transmitted to the feed rollers via a gear to feed out the wire held between the feed rollers. As illustrated in FIG. 15 by way of example, a roller 22a' is held by a slide 33' located in a radial movable manner on a crank disc 22' fixed to a crank spindle 21', and is moved and positioned by an adjust screw 34'. In operative association with the rotation of the crank disc 22', the roller 22a' is moved within a guide groove 32a' provided in a segment gear 31', whereby the segment gear 31' is rocked, while its angle of rotation around its shaft 31a' is limited to a given value, thereby providing a repeated rotation of a pinion 30 in mesh with the segment gear 31'. The force of rotation of the pinion 30 is transmitted to a one-way rotary shaft 28 via a one-way clutch 29 to rotate the feed roller via a gear (not shown) in one direction alone. It is noted in this connection that the angle of rocking of the segment gear 31' is immediately proportional to the length of the wire fed out. In order to regulate the length of the wire fed out, it is required to restrict an angle defined by two tangential lines drawn from the center of the shaft 31a', acting as the fulcrum of the segment gear 31' adapted to move the roller 22a' placed on the crank disc 22' in its radial direction, to an orbit in which the roller 22a' rotates around the axis of the crank spindle 21'. More specifically, the two tangential lines are drawn from the center of the shaft 31a' to a circle a locus illustrated by the center of the roller 22a'. Therefore, if an angle defined between the two tangents is small, a length of the wire fed out is small because the segment gear 31' is rotated at an angle proportional to the angle defined between the two tangents. It is then necessary to change the angle defined between the two tangents by moving the roller 22a' toward or opposite the center of the crank spindle 21' when it is necessary to change the length of the wire fed out.
As illustrated in FIG. 14, the portion for operating a pitch tool 17 includes an L-shaped pitching lever 14 pivotally fixed to the apparatus proper, which has the pitch tool 17 at one end. The pitching lever 14 always receives at one end a one-way moment of rotation from the force of a spring 15 and is fixed at the other end by a stopper 16' for determining the position at which the pitching lever 14 is to be stopped. Then, a connecting rod 11' is provided to rotate the pitching lever 14 against the force of the spring 15. Connected to a second lever 10' including a stroke controlling block 10a' caused to follow a main lever 2a' of a follower 2' of a cam unit 1', this rod 11' is vertically displaceable in FIG. 14. When, as shown in FIG. 14, the connecting rod 11' is moved upwardly by the force of the spring 15 to bring the pitching lever 15 in abutment against the stopper 16', the pitch tool 17 mounted on one end of the pitching lever 14 is so retracted to the reference position that the follower 2' of the cam unit 1' is spaced away from a pitch cam 4'. Thus, as the follower 2' of the cam unit 1' is pushed down by engagement with the pitch cam 4', the connecting rod 11' is moved so downwardly that the pitching lever 14 is rotated clockwise to thrust out the pitch tool 17. According to such an arrangement, the crank spindle 21' for rotating the crank disc 22' of the wire feeding portion rotates in synchronism with a cam shaft 3 to which the pitch cam 4' of the cam unit 1' of the pitch tool operating portion is fixed.
With such an apparatus, pitched helical springs have heretofore been produced by thrusting out the pitch tool 17, while the wire continuously fed out of the wire feeding portion by a given length is brought in engagement with the bending die.
The thus produced compression coiled spring is to be placed at each end on a horizontal and thus includes a so-called seat turn in close contact with the adjacent turn. The seat turn is provided to stabilize the coiled spring when placed on a horizontal, and usually comes in contact with a horizontal over about 3/4-4/5 of its length. In the process of the wire being coiled form the seat turn at a given pitch, the coil's end is brought in contact with the adjacent turn by an initial tension. Of importance to keep the coiled spring upright is that the coiled spring be formed such that its axis makes a right angle (hereinafter called the squareness of the seat turn) to a horizontal inclusive of the seat turn. The conventional technique for producing coiled springs with such apparatus as mentioned above, however, is too time consuming and laborious to vary the shape and size of straight or taper compression coiled springs in such items as total number of turns, amount (or number) of seat turns, pitch and the squareness of seat turns for various reasons to be described later. Thus, this technique is not only low in working efficiency but makes it difficult to make regulations depending upon the processes applied. What is more, arrangements for producing compression coiled springs of high accuracy take very much time.
(1) The amount of the seat turn of the coiled spring produced with the conventional apparatus, an schematic illustration of which is given in FIG. 14, is determined by an angle value found by subtracting an amount of an angle of the follower 2', while it is in engagement with the pitch cam 4', from an amount of an angle of the pitch cam 4' rotated from the time when wire feeding is initiated to the time when wire feeding is terminated. Explaining this with reference to he compression coiled spring to be produced having an increased pitch, the adjust screw 11a' which is a right-hand thread screw and is screwed into the upper end of the connecting rod 11' is first turned to let it down, thereby narrowing a space between the end of the pitching lever 14 having the connecting rod 11' inserted through it and the second lever 10'. In consequence, the position at which the follower 2' begins decending by engagement with the pitch cam 4' comes close to the base circle of the pitch cam 4' to increase a vertical displacement of the connecting rod 11', whereby the amount of the pitch tool 17 to be thrusted out is increased. Thus, there is an increase in an amount of the angle of the pitch cam 4' rotated while the follower 2' is in engagement with the pitch cam 4', but there is a decrease in the amount of the seat turn, correspondingly. In order to obtain the proper amount of the seat turn, say, about 4/5-3/4 turn, it is thus required to regulate the positions of axially two-divided pitch cams 4' and 4' by loosening a lock nut provided on the cam unit 1'. However, this takes much time, since the operation should be suspended to repeat fine regulations. In order to obtain the proper amount of the seat turn without regulating the pitch cams 4' and 4', the following technique is proposed. According to this technique, the adjust screw 10b' is turned to move the stroke controlling block 10a' on the side of the fulcrum around which the second lever 10' rocks, so that the position at which the follower 2' begins descending by contact with the pitch cam 4' comes close to the base circle of the pitch cam 4', thereby increasing a vertical displacement of the connecting rod 11'. In this state, the adjust screw 11a' is turned left to delay the time when the pitching lever 14 is to be actuated, thereby returning the amount of the pitch tool 17 to be thrusted out to a given amount to obtain a given pitch and return the amount of the seat turn to the initial. Such regulation of the amount of the seat turn, however, still suffers from a disadvantage that the squareness of the seat turn is not precise. This is because the angle of rotation of the pitch cam 4' is so unvaried in the process of the seat turn pitch changing to a given pitch that the rates of the pitch tool 17 thrusted out and retracted, while the seat turn pitch changes to a given pitch, are rapider than they were before the regulation. In most cases, the positions of the pitch cams 4' and 4' should finally be re-regulated.
When the pitch of the coiled spring to be produced has a decreased pitch, the adjust screw 11a' is turned left to let it up, thereby enlarging a space between the end of the pitching lever 14 having the connecting rod 11' inserted through it and the second lever 10'. In consequence, the position at which the follower 2' begins descending by contact with the pitch cam 4' is spaced away from the base circle of the pitch cam 4', so that the vertical displacement of the connecting rod 11' is decreased to decrease the amount of the pitch tool 17 in thrusting out. This also gives rise to a phenomenon similar to that associated with the coiled spring having an increased pitch.
When the wire to be used to produce the coiled spring varies in length, there is a variation in the amount of the seat turn. Briefly, the reason is that since the angle of rocking of the segment gear 31' varies, the times at which wire feeding is to be initiated and terminated vary with respect to the pitch cam 4' of the cam unit 1' rotated in synchronism with the crank disc 22' for rocking the segment gear 31'. This will be explained later in greater detail. As a matter of course, it is then required to re-regulate the amount of the seat turn by such means as mentioned above. Thus, the results of regulations of length of the wire fed out (the total number of turns), amount and squareness of the seat turn, the pitch, etc. have mutual contradictory influences upon the shape and size of the coiled spring to be produced, resulting in frequent re-regulations. In addition, the operation should be suspended whenever each regulation is carried out. The reasons are that (1) the positions of the pitch cams 4' and 4' and the angle of reciprocation of the segment gear 31' for varying the length of the wire fed out should be regulated within the apparatus, and the adjust screw 10b' is positioned at a distance about three times as large as the distance from the fulcrum of the second lever 10' to the junction of the connecting rod 11'. Such regulations are much laborious and need skillfulness since they are carried out on the basis of workers' intuition.
(2) The length of the wire fed out to produce the coiled spring is varied by regulating an amount of the angle of reciprocation of the segment gear 31'. As already mentioned, this angle is defined by two tangential lines drawn from the shaft 31a' that is the fulcrum of the rocking segment gear 31' to an orbit in which the roller 22a' rotates around the axis of the crank spindle 21'. In association with the regulation of the position of the roller 22a', there is a variation in the time at which the rate of the segment gear 31' is zero with respect to the rotation of the crank disc 22', i.e., in the time when wire feeding is to be initiated or terminated. Also, that time varies with respect tot he rotation of the pitch cam 4' rotating in unison with the crank disc 22' and, hence, with respect tot he time when the pitch tool 17 is to be thrust out or retracted, so that any proper length of the seat turn cannot be obtained. Thus, it is required to re-regulate the amount of the seat turn by such means as mentioned above.
(3) The wire used to produce the coiled spring is of an elastic and plastic material. For pitching, it is required to thrust out the pitch tool 17 excessively so that the pitch of the desired coiled spring is slightly exceeded to accommodate to springing-back. However, during the transition from the leading seat side of a coil to a given pitch, coiling takes place, while the pitch tool 17 is thrust out as the follower 2' is moved away from the base circle of the pitch cam 4' along the outer periphery of the pitch cam 4'. During the transition from a given pitch to the trailing seat turn of the coil, coiling takes place, while the pitch tool 17 is retracted as the follower 2' is moved toward the base circle of the pitch cam 4' along the outer periphery of the pitch cam 4'. Although the conditions are quite contradictory to each other in this manner, it is required to make use of the pitch cam 4' shaped following the curvature change required to prevent a jumping-up of the follower 2'. This makes it impossible to effect both the extension and retraction of the pitch tool 17 at a uniform speed. Besides, there is only a set of the main lever 2a' and second lever 10' etc. having direct relation to the squareness of the seat turn. In most cases, therefore it is very difficult to impart a correct squareness to each seat turn of a compression spiral spring. For that reason, a plurality of pitch cams 4' differing in outer curvature are provided as reference pitch cams. In most cases, however, said pitch cams 4' are unserviceable for the desired compression coiled spring, since such compression springs are of different pitches, diameters of coils, materials thereof etc. and they are varied in types. In such cases, the outer periphery of the pitch cam 4' is repeatedly cut as by a hand grinder to correct the outer curvature of the pitch cam 4'. However, such a pitch cam 4' only serves as an exclusive cam for the next arrangements.
When producing such a taper compression spiral spring as shown in FIG. 13(b), various regulations for obtaining such proper seat turns as mentioned above are more laborious than those required for straight compression spiral springs, since there is an increase in the amounts of both the seat turns because they differ in the diameters thereof. In the case of forming compression spiral springs, a suitable initial tension is usually applied to the ends of a coil in order to stabilize the seat turns and a free length. Because the greatest outer diameters of the pitch cams 4' and 4' are shaped to contours having the same radii and the pitch tool 17 is extended by a given amount to a given position, such a taper compression coiled spring as shown in FIG. 13(b) has a pitch decreased under the influence of the initial tension applied to the coil ends, as the coil diameter is increased. Pitching for obtaining the theoretical load characteristics originally required takes much time.
(4) A wire formed of a material for coiled springs by cold drawing cannot always be formed into a compression coiled spring of the desired shape and size even with an exclusive cam for the next arrangements, since there is a variation in the material properties. It is then required to provide repeated regulations of such parts as mentioned above. Even though the compression spiral spring of the desired shape and size can be formed with said exclusive cam, it would likewise take much time to replace the two-split type of pitch cams 4' and 4' and to position them.